The long range objective of this project is to understand the activity of sympathetic preganglionic neurons (SPNs) and to clarify the spinal circuitry involved in the orderly transfer of neural information to and from these neurons. Three types of synaptic potentials and their putative transmitters were identified for the first time in the rat SPNs during this granting period. Studies proposed in this renewal application will address the cellular mechanisms underlying the actions of putative transmitters responsible for generating the fast and slow excitatory postsynaptic potentials (EPSPs) in the SPNs and the intracellular signal transduction associated with the activation of appropriate receptors by these transmitters. Current and voltage clamp studies will be performed on identified SPNs of the transverse spinal cord slices removed from neonatal (15.20 days old) rats; whole-cell- patch recordings will be obtained from labeled, acutely dissociated SPNs. Labeling will be accomplished by injecting rodamine latex microspheres into the superior cervical ganglia of young (45-60 days old) rats 4.5 days prior to experimentation. The proposed study has the following major objectives. First, the contribution of Ca+ Na and K ions to the inward current induced by N-methyl-D- aspartate (NMDA) and putative transmitters glutamate and aspartate responsible for the fast EPSP will be ascertained. Second, the electrophysiological characteristics of the outward current immediately following the NMDA-induced inward current will be studied. Third, the type(s) of K current responsible for the slow EPSP and the slow depolarization induced by putative transmitters norepinephrine (NorePi) and substance P (SP) will be characterized. Fourth, the hypothesis that the closure of K channels by Norepi and SP is linked to the inositol triphosphate/diacylglycerol-protein kinase C (PI-KC) system will be evaluated by analyzing the dose- effects of PI-KC activators phorbol esters and diacylglycerol analogs on the K current determined in objective 3. Fifth, the regulation of Ca current induced by NMDA and excitatory amino acids by phorbol esters and diacylglycerol analogs will be studied. Lastly, the modulation of NMDA-induced inward current and the fast EPSP by glycine will be analyzed. Delineating the mechanism of action of putative transmitters and the role of intracellular second messengers will lead to better understanding of information processing in the SPNs, and contribute to rational design of drugs aimed at controlling hypertension and related cardiovascular diseases.